1. Field of the Invention
The present invention relates generally to display devices (so-called display cells) for use with a large screen display apparatus and particularly to a display device for use with an indoor-type large screen display apparatus employing a cathode ray tube.
2. Description of the Prior Art
In the prior art, a large screen display apparatus is constructed by assembling a plurality of existing television receivers in the vertical and horizontal directions as shown in FIG. 1 or the large screen display apparatus is constructed by assembling a plurality of liquid crystal display devices similarly as described above.
Alternatively, as shown in FIG. 2, an 8-element display device 35 or the like is proposed (see Japanese Patent Laid-Open Gazette No. 60-191703). According to the 8-element display device 35, a plurality of, for example, 8 sets of fluorescent trios 34, each formed of green, red and blue three primary color fluorescent layers G, R and B forming a pixel are provided within a glass tube envelope 33 formed of a front panel 31, a rear panel (not shown) and a side plate 32. The display devices 35 are arranged in a two-dimensional manner, thereby forming a large-sized display apparatus as shown in FIG. 1 or 2. This type of large-sized display apparatus provides sufficient brightness so that it can reproduce a clear visual image even outdoors.
Further, as the large screen display apparatus, a matrix display is known, in which a cathode ray tube 36 is utilized as a display cell as shown in FIG. 3.
In the prior-art large screen display apparatus formed of display devices, for example, in the large screen display apparatus in which a plurality of cathode ray tubes 41 are provided as shown in FIG. 1, however, a connected portion between the adjacent cathode ray tubes 41 and 41 causes a cross bar 42, which deteriorates the quality of image considerably. More specifically, as shown in FIG. 4, in the case of the cathode ray tube 41 formed by the tube envelope which is comprised of a panel 44 of non-flat plate shape having a fluorescent screen 43 formed on its inside surface and a funnel portion 45, a panel-funnel connected portion needs a proper thickness t.sub.1 from a mechanical strength and dielectric strength standpoint. For example, the limit of the thickness of, for example, a 4-inch cathode ray tube falls in a range of from 2.5 mm to 3 mm. As a result, a useless portion l between the adjacent cathode ray tubes 41 and 41 is large and this large useless portion l becomes a cross bar, resulting in the image quality to be deteriorated. In FIG. 4, reference letter m represents the effective portion.
As shown in FIG. 5, a viewfinder for a video camera utilizes a cathode ray tube 54 wherein a tube envelope 53 is formed of a flat panel 51 of flat-shaped glass and a funnel portion 52. In FIG. 5, reference letter 55 designates a fluorescent screen, and 56 an electron gun. Generally, a viewfinder of about 0.7-inch is applied with a high voltage of less than 5 kV, for example, 2 kV so that a thickness t.sub.2 of the funnel portion 52 of the tube envelope thereof is sufficient of about 1 mm from a mechanical strength and dielectric strength standpoint. However, if this type of viewfinder is formed as 4-inch type or the like, then this 4-inch type viewfinder needs large mechanical strength and dielectric strength with the result that the funnel of about 1 mm thick can not be employed.
In the large screen display apparatus shown in FIG. 2, each of the fluorescent trios 34 is formed as a rectangular strip configuration and the longitudinal direction of the fluorescent trios 34 is aligned in the vertical direction of the display screen so that the following problems arise. As, for example, shown in FIG. 6, when the viewer watches the picture screen from a relatively lateral direction relative to the display picture screen (this situation is inavoidable when many viewers watch the same display screen because a space in which the display apparatus is located indoors is small), of the fluorescent trio series 34l and 34r existing at respective sides of the picture screen, the fluorescent series located at the endmost of the picture screen are hidden by a frame 37, so that the fluorescent trio series 34l and 34r existing at the respective sides can not function to display a visual image. More specifically, as shown in FIG. 6, in the case of a viewer Hl who watches the picture screen from the left-hand side, of the leftmost fluorescent trio series (area shown by a one-dot chain line) 34l, the leftmost fluorescent series G is hidden by the frame 37, whereby the visual image displayed by the fluorescent trio series 34l does not appear to have natural color but has a predetermined color (magenta, which should be originally white) for the viewer Hl. The above-mentioned fluorescent trio series 34l does not function as a fluorescent trio for displaying the visual image. This is also true for a viewer Hr who watches the picture screen from the right-hand side. That is, the fluorescent trio series 34r located in the rightmost position of the picture screen appears to have a predetermined color (in that case, yellow), and can not function as the fluorescent trio by which the visual image is displayed.
Accordingly, when the large screen display apparatus is constructed by the conventional display elements, a visual field A.sub.1 of the visual image distant by a predetermined distance n of the display apparatus must be considered in practice excepting the fluorescent trio series 34l and 34r at the respective side ends so that the visual field A.sub.1 is reduced to a visual field A.sub.2 as shown in FIG. 6. Therefore, the function (to enable to many viewers to watch the same large screen) of the large screen display apparatus can not be demonstrated sufficiently.
Further, as shown in FIG. 2, the glass tube envelope 33 has to have a sufficient thickness from a mechanical strength and dielectric strength standpoint, and thus a resolution can not be sufficiently increased by reducing the pitch of the fluorescent trio 34.